Pull-type harvesting implements have been utilized for harvesting operations for many years. These harvesting implements can have a variety of configurations, but generally have a transverse frame to which is connected a pivotal draft member or tongue. The draft tongue extends forwardly of the transverse frame for attachment to a prime mover, such as a tractor, which provides all operative power for the implement. The tractor provides motion to the implement, as well as power for operating the harvesting components supported by the implement frame.
One such pull-type configuration is the pivot tongue windrower, such as seen in U.S. Pat. No. 5,272,859, issued to Martin E. Pruitt, et al on Dec. 28, 1993, the descriptive portions of which are incorporated herein by reference. This '859 patent also teaches the mounting of a central gearbox on the header such that the gearbox is movable relative to the implement frame. This gearbox is rotatable about a generally vertical axis so that the input shaft into the gearbox can generally follow the pivotal movement of the centrally pivoted draft tongue.
To accomplish the coordinated movement of the rotation of the gearbox with the pivotal movement of the tongue, the '859 patent discloses a telescoping steering mechanism that interconnects the tongue and the gearbox such that the gearbox is rotated in response to the transverse movement of the draft tongue. The telescopic action of the steering mechanism is operable to accommodate the changes in distance of the respective connecting points thereof with the tongue and the gearbox as the tongue swings from side to side, due to the different horizontally spaced pivot centers of the draft tongue and the gearbox. The telescopic action of the steering mechanism, along with a generally horizontal pivot or gimble, also allows the steering mechanism to follow the vertical movement of the header relative to the tongue without restricting the movement of the header or the draft tongue.
This steering mechanism, as taught by the '859 patent, suffers from operational problems associated with vibration due to the loosely fitting telescopic parts and wear of the sliding parts. The implement, as can be seen in the drawings of the '859 patent, is provided with rotatable cutting mechanism and crop conditioning mechanism. The operation of these harvesting components provides a substantial amount of vibration within the implement. Since the steering mechanism is loosely constructed to permit the necessary relative pivotal movements of the header and the draft tongue, this operational vibration causes noise and wear in the parts of the steering mechanism. Furthermore, the looseness of the parts and the sliding action therebetween causes substantial wear in the steering mechanism, resulting in the increased likelihood of failure.
Furthermore, the mechanism of the '859 patent is subject to side forces from the torque applied to the gearbox by the drive mechanism and the cutterbar forces within the crop harvesting header on which the rotatable gearbox is mounted. These external forces place a side load on the steering link and can result in a binding of the telescoping tubes forming the steering link, which results in a thrust load on the gearbox and the connecting apparatus, particularly when the header rises and the telescopic tubes telescope together. These telescoping tubes also present a hinge-like degree of freedom which can contribute to the vibration in the apparatus.
Utilization of a hydraulic master/slave cylinder arrangement, with the master cylinder associated with the pivoted draft tongue and the slave cylinder effecting a corresponding movement of the rotatable gearbox, is also subject to the side forces from the torque applied to the gearbox by the drive mechanism and the cutterbar forces within the crop harvesting header on which the rotatable gearbox is mounted. A variation of the master/slave hydraulic arrangement would be single-acting master and slave cylinders coupled with a spring to oppose the slave cylinder attached to the gearbox. A problem encountered with such a system is that the external forces can overcome the spring coupled with the hydraulic mechanism and force the gearbox from the correct position, causing the gearbox input shaft to bend. Another problem encountered with the master/slave hydraulic mechanism is that hydraulic fluid leaks across the cylinder pistons causing the slave cylinder to fall out of synchronization with the master cylinder and, thereby, possibly resulting in the gearbox being turned at an improper angle.